This invention relates to a system for applying a liquid, such as glue, in a thin stream onto a web of paper as it is moving through a printing press. The system provides a mechanism for purging the liquid from the applicator after each application to prevent clogging of the applicator.
There are presently on the market systems which apply a thin stream of glue or paste, or backbone softening liquid to a web of paper as it is moving through the press. The applicator is usually positioned immediately ahead of the folding mechanism which folds the web into the configuration desired so that the portions of the web are glued together. The type of systems presently on the market utilize applicators which resemble hypodermic needles to apply the liquid paste or glue. When the application is completed, the applicator has to be quickly disassembled and purged otherwise the glue will solidify in the fine conduit, causing cleaning problems and possibly replacement of the needle-like applicator.
This can be a considerable problem because it may be necessary on occasions to shut down the press in the middle of the application, and if the press is off for any length of time, the glue may thicken or solidify in the applicator.
It is an object of this invention to provide a means for readily purging the applicator whenever the applicator is not being used so that the liquid will not remain in the applicator and will not tend to thicken or dry and clog the applicator. With this system, the applicator is always clean and ready for use.
The system not only provides for purging of the applicator, but it provides the purging in a novel and safe manner which will protect the press operator from being injured by the needle-like applicator and also it provides a shielding for the rather fragile applicator tip so that it will not be damaged while the applicator is in use.
In accordance with this invention, an applicator is provided for applying a liquid such as a glue or backbone softening liquid to a web of paper so that web is moving through a printing press. The applicator comprises along, thin needle-like dispensing tip, a liquid supply line, a gas purge line and means for alternately connecting the liquid supply line and the gas purge line to the dispensing tip. When the liquid supply line is connected to the tip, the tip will be arranged to dispense liquid and when the gas purge line is connected, the tip will be purged of the liquid. A shield means is provided to at least partially surround the tip when the tip is connected to the gas purge line.
The applicator has a body member having first and second fluid conduits extending therethrough for connecting to the separate gas and liquid sources. A head member is mounted for movement relative to the body. This head member is preferably journaled for rotation relative to the body, and the head member has a fluid conduit therethrough which is aligned with the first fluid conduit in the body member in a first relative position of the members and is aligned with the second fluid conduit in the body member in a second relative position of the members. The fluid dispensing tip is mounted on the head member, and means is provided for effecting movement of the members between their first and second relative positions, so that in the first position fluid may be discharged from the tip and in second position the tip may be purged of the liquid.
The shield may be mounted on the body member, which is preferably stationary, and this shield extends over and in front of the dispensing tip when the tip has been moved to its position in fluid communication with the purge line. The tip preferably extends parallel to the axis of rotation of the head and the shield extends parallel to the tip so that when the tip is rotated to its purging position, it will be substantially contained within and protected by the shield.